The long-range purpose of the project is to study the biochemistry, morphology, pharmacology and physiology of inner ear neurons and other cells and to describe the mechanisms of their interactions. 1. Two-dimensional electrofocusing/electrophoresis has been applied to the analysis of cochlear proteins after in vivo labeling and may provide a very sensitive approach of the study of cochlear function. 2. Enkephalin-like immunoreactivity, visualized as immunofluorescence, has been demonstrated in the two olivocochlear, efferent neuronal systems of the organ of Corti in guinea pig and cat. No such immunoreactivity was found in hair cells of the organ of Corti, or in the auditory nerve. 3. DL-alpha-aminoadipate in the cochlea at high concentrations does not change click evoked auditory nerve compound action potentials. This implies that the postsynaptic receptor of the hair cell-auditory nerve synapse is not of the N-methyl-D-aspartate, aspartate-preferring type.